An instrument as is set forth in the opening paragraph is in particular suitable for minimally invasive surgery, in course of which, usually, an elongated mechanism having substantially small cross-section is introduced via an incision into a body of a patient. The mechanism may comprise a handle or any other suitable actuator or mechanism for operating the first and the second working elements, for example, miniature forceps, miniature scissors, or the like. It is of paramount importance to first, apply sufficient force to the first and the second working element on one hand, and to provide accurate feedback of the applied force to the operator.
An embodiment of an instrument for minimally invasive surgery is known from WO 03/020139. In the known instrument the external force exerted on the forceps by a surgeon is being measured by a force sensor arranged on a jaw of the forceps and is feed-back to the surgeon via a control unit. In this way the surgeon can have a feeling of the applied force. The force sensor may be connected by means of a glass fiber to a suitable control unit.
It is a disadvantage of the known instrument in that an accuracy of the force measurement is affected by external factors, like ambient temperature and signal loss caused by undesirable deflection of the fiber due to the fact that it runs over a hinge of the working element. It is a further disadvantage of the known instrument that the gripping force measurement by the force sensor on the forceps is dependent on the axial position of the tissue in the forceps.
Another embodiment of a surgical instrument is known from U.S. Pat. No. 6,616,667. It is a disadvantage of the known surgical instrument that force sensor signals are routed along hinges, which decreases accuracy of the measurement.
A still another embodiment of a surgical instrument is known from WO2007/111737. It is a disadvantage of the known surgical instrument that, by way of its construction and sensor arrangement, it cannot measure gripping force independently of a position of tissue in the jaws.